Can anyone help me. I just had my DAR inspection and am ready to fly. I built my RV-12 as a home build so I bought an engine with 20 hours on it. I had a small leak at the fuel pump so I elected to buy a new pump. Now while I was doing my static RPM test my fuel pressure drops to 1.1 lb. at higher RPMs. I sent for another new fuel pump. Now the new pump is putting out 6.2 lbs at idle. I'm told I should not go over 5.5 lbs. Is this normal to have 2 bad pumps? Both pumps came from Lockwood.
Van's Air Force
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Rotax 912 Fuel Pump Pressure
- Thread starter johns4689
- Start date
More info please..............
Is the rest of your fuel system as per the plans? Was the electric pump on or off during these tests? This engine you bought - does it have the same provisions for returning unused fuel to the tank as the Van's supplied engine? Are you sure that is working? When you run the electric fuel pump without the engine running is fuel actually being returned to the tank?
Sorry if this sounds like the "fifth degree", but I think anyone trying to help you will need more information.
John
Is the rest of your fuel system as per the plans? Was the electric pump on or off during these tests? This engine you bought - does it have the same provisions for returning unused fuel to the tank as the Van's supplied engine? Are you sure that is working? When you run the electric fuel pump without the engine running is fuel actually being returned to the tank?
Sorry if this sounds like the "fifth degree", but I think anyone trying to help you will need more information.
John
fuel pressure sensor is not very accurate
What is the fuel pressure of the second new fuel pump at high RPM?
The Rotax manual says 5.8 PSI is the maximum allowed. I wonder what the danger is of too high pressure, mechanical damage to the carburetor or forcing fuel past the float valve causing flooding?
With all of the problems that some builders are having with vapor lock, I would leave the higher pressure pump installed. The Dynon fuel pressure sensor is not very accurate. It only costs about $35. A high quality industrial sensor can cost several hundred dollars. I would not trust the Dynon fuel pressure reading unless it was verified to be accurate by comparing to a calibrated gauge. The fuel pressure readout tells you that the fuel pump is working. But the actual value is meaningless unless verified.
Since the new pump is made for the Rotax 912 and sold by Lockwood, it should be OK to use, especially if it is the new and improved model. But to be safe, measure the fuel pressure with an accurate and calibrated gauge or sensor.
Joe Gores
What is the fuel pressure of the second new fuel pump at high RPM?
The Rotax manual says 5.8 PSI is the maximum allowed. I wonder what the danger is of too high pressure, mechanical damage to the carburetor or forcing fuel past the float valve causing flooding?
With all of the problems that some builders are having with vapor lock, I would leave the higher pressure pump installed. The Dynon fuel pressure sensor is not very accurate. It only costs about $35. A high quality industrial sensor can cost several hundred dollars. I would not trust the Dynon fuel pressure reading unless it was verified to be accurate by comparing to a calibrated gauge. The fuel pressure readout tells you that the fuel pump is working. But the actual value is meaningless unless verified.
Since the new pump is made for the Rotax 912 and sold by Lockwood, it should be OK to use, especially if it is the new and improved model. But to be safe, measure the fuel pressure with an accurate and calibrated gauge or sensor.
Joe Gores
Mark Henderson
Well Known Member
Rotax owners has a video on checking fuel pressure. They use a simple mechanical gauge to check things. Part of the problem with the setup we have is the sensor goes up to 35 psi if I remember correctly. Since we are only interested in the first 6 or so lbs it is less accurate. A 0-10 psi. sensor would be better, unless as Joe said, you are using a high end sensor.
Rather than put in the dual Dynon system, I am in the process fitting a new Right instrument panel which has an ASI, Altimeter, Uma mechanical oil pressure and fuel pressure gauges, and a Monroy ATD-300 traffic alert. The fuel pressure is a 0-10 psi. I am moving the oil pressure sensor to the firewall and will T off it for the new oil pressure gauge. The reason I am going just with these 2 for the moment it it seems the majority of the problems others have experienced so far have been faulty fuel and oil pressure readings. If my Dynon suddenly says I've lost oil pressure but the mechanical still reads full pressure, I will know what do do. At least one 12 has made an emergency landing due to no oil pressure on the Dynon. It was in fact the sensor failing.
Rather than put in the dual Dynon system, I am in the process fitting a new Right instrument panel which has an ASI, Altimeter, Uma mechanical oil pressure and fuel pressure gauges, and a Monroy ATD-300 traffic alert. The fuel pressure is a 0-10 psi. I am moving the oil pressure sensor to the firewall and will T off it for the new oil pressure gauge. The reason I am going just with these 2 for the moment it it seems the majority of the problems others have experienced so far have been faulty fuel and oil pressure readings. If my Dynon suddenly says I've lost oil pressure but the mechanical still reads full pressure, I will know what do do. At least one 12 has made an emergency landing due to no oil pressure on the Dynon. It was in fact the sensor failing.
Joe is right. You need to get a handle on actual fuel pressure. While a quality instrument would be ideal, consider picking up an inexpensive unit at an auto parts store and tee-ing into the line just upstream of your Dynon FP sensor. Then see how that reads in comparison with electric only and with engine on.Even without metaphysical certainty, you should have some idea whether the pumps are performing within spec.
My experience is that the Dynon will *never* show the same readings on two consecutive flights even if all other conditions are identical. I believe they are actively seeking a source for an affordable, low-range FP sensor.
Jim
#264 flying >25 hours
My experience is that the Dynon will *never* show the same readings on two consecutive flights even if all other conditions are identical. I believe they are actively seeking a source for an affordable, low-range FP sensor.
Jim
#264 flying >25 hours
RDOG
Well Known Member
I don't know of any vapor lock problems. Where did you see a vapor lock problem?
I just got back from running the 12 again. The fuel does return to the tank with the electric pump running and the engine off. With the engine running I got 6.2 to 6.4 lbs. of pressure. At hight rpm's I got the same thing. I am using a GRT EIS and not the Dynon. I can't belive it would be the sensor. I think I'll try putting the 1st new pump back on and see if it still reads low.
I think I have it narrowed down. I just checked the first pump and found it had a broken spring, I think that's why the pressure dropped ast hight rpm. I switched springs and both pumps run at about 6 lbs. I found the orifice in the return line to be (35). I assume that's .35 thousants. What size should it be?
Vapor lock
http://www.vansairforce.com/community/showpost.php?p=521820&postcount=16
and Marty had a similar problem.
http://www.vansairforce.com/community/showpost.php?p=543934&postcount=20
Jim is convinced that he had vapor lock due to the high TX heat and fuel properties.
Marty has not determined the cause of his engine problem yet, but from the symptoms, I believe it is vapor lock, the same as Jim.
Higher fuel pressure and lower temperatures help to prevent vapor lock.
Joe Gores
Ask Jim (N223JH in the post above yours) about his engine quitting and see:
http://www.vansairforce.com/community/showpost.php?p=521820&postcount=16
and Marty had a similar problem.
http://www.vansairforce.com/community/showpost.php?p=543934&postcount=20
Jim is convinced that he had vapor lock due to the high TX heat and fuel properties.
Marty has not determined the cause of his engine problem yet, but from the symptoms, I believe it is vapor lock, the same as Jim.
Higher fuel pressure and lower temperatures help to prevent vapor lock.
Joe Gores
RDOG
Well Known Member
It is my opinion that these are fuel pump problems. With the Rotax release of the new pump this week to combat the high pump failure rate, replacing the pump is the first place to look to fix the problem. The fix for high fuel flow low pressure would be to replace the pump like we did. Problem solved, 25hrs on new pump no problems.
With fuel constantly flowing through the lines back to the tank where would the vapor lock occure?
Colin is right...its in the fuel pump. The regulator for fuel pressure is inside of the fuel pump. The earlier SB to replace fuel pumps (before the 12) was because the regulator couldn't manage additional pressure from a boost pump. Supposedly it was fixed. Now we have a new pump that looks like an aircraft part instead of a Renault part. I would wait a bit on buying a new sender.
vapor lock explained
When the engine demands more fuel at full throttle, it can be starved if part of the fuel is escaping out of the carburetor vents as vapor.
I can think of 3 ways to prevent vapor lock:
1. Use a fuel that is less prone to vapor lock. (Fuels containing alcohol or winter additives evaporate easier.)
2. Increase the fuel pressure by using a better pump (like RDOG did).
3. Keep the fuel system cool with insulation or shrouds or cooling air.
Joe Gores
I agree with you. Like I said in my previous post, higher fuel pressure and lower temperatures help to prevent vapor lock. The new pump puts out more pressure to help prevent vapor lock. The word LOCK is a misnomer. The fuel is not locked or blocked. Actually in a vapor lock situation, the fuel actually flows faster and the pressure drops. The reason for this is that the fuel forms little vapor bubbles in the fuel line. Since a mixture of fuel vapor and liquid flows easier than pure liquid, the flow increases. In addition, the fuel vapor escapes out of the carburetor vents, which also increases the flow. Also, the mixture of fuel vapor and liquid can more easily flow through the return line orifice back to the tank. The pressure drops because there is less resistance to flow. An analogy is a garden hose. If allowed to flow freely, the flow rate is high but the pressure is low. But hold your thumb over the end of the hose to restrict flow and the pressure goes up, causing the water to squirt further.
When the engine demands more fuel at full throttle, it can be starved if part of the fuel is escaping out of the carburetor vents as vapor.
I can think of 3 ways to prevent vapor lock:
1. Use a fuel that is less prone to vapor lock. (Fuels containing alcohol or winter additives evaporate easier.)
2. Increase the fuel pressure by using a better pump (like RDOG did).
3. Keep the fuel system cool with insulation or shrouds or cooling air.
Fuel constantly circulating back to the tank helps to keep the fuel cool. However fuel obeys the laws of physics. It will evaporate if the conditions are right, depending on the properties of the fuel, the temperature and pressure.
Joe Gores
Jetguy
Well Known Member
Oh those little bubbles!
This is where I'm confused. What are these properties or conditions? Marty lives in IA. I'm sure it wasn't very hot when he was flying when his problem occurred. I agree it could be something in the fuel depending on different things like how old, how stored, etc. A small leak in a fuel line may induce bubbles but I wonder about that Pump cavitation. That could cause problems for sure. Maybe this new pump will help out in that respect.
This is where I'm confused. What are these properties or conditions? Marty lives in IA. I'm sure it wasn't very hot when he was flying when his problem occurred. I agree it could be something in the fuel depending on different things like how old, how stored, etc. A small leak in a fuel line may induce bubbles but I wonder about that Pump cavitation. That could cause problems for sure. Maybe this new pump will help out in that respect.
DonFromTX
Well Known Member
Winter or summer blending could play a role, we are getting these problems in the spring you know. Left over winter blended fuel maybe?
It COULD be that there are "hot spots" under the cowling overheating some portion of the fuel system from exhaust heat or heated cooling airflow.
It COULD be that there are "hot spots" under the cowling overheating some portion of the fuel system from exhaust heat or heated cooling airflow.
Cavitation?
I must have missed something... When was cavitation determined to be the problem with the engine-driven fuel pump? Does this mean air is leaking into the system creating air vapor? All my discussions with Rotax techs regarding my power loss were in regard to a failure mode which would release fuel via the weep holes...generating a noticable fuel odor. Oh yes, and Rotax was adamant that the FP has no intermittant failure mode. I was told if it was leaking it was bad, if it wasn't leaking and generating minimum FP it was good.
If anyone has definitive information about EDFP partial failure I would sure like to hear about it. My power losses were always associated with a hot engine, hot ambient, winter gas, low fuel pressure and high fuel flow, full power.
Jim
#264 flying >25hours
I must have missed something... When was cavitation determined to be the problem with the engine-driven fuel pump? Does this mean air is leaking into the system creating air vapor? All my discussions with Rotax techs regarding my power loss were in regard to a failure mode which would release fuel via the weep holes...generating a noticable fuel odor. Oh yes, and Rotax was adamant that the FP has no intermittant failure mode. I was told if it was leaking it was bad, if it wasn't leaking and generating minimum FP it was good.
If anyone has definitive information about EDFP partial failure I would sure like to hear about it. My power losses were always associated with a hot engine, hot ambient, winter gas, low fuel pressure and high fuel flow, full power.
Jim
#264 flying >25hours
MartySantic
Well Known Member
I indeed had winter gas and the temperature that day was in the upper eighties. So based on the conversation with the tech at LEAF (they have seen this condition previously), the data from my Dynon (wild pressure and fuel flow variations), it appears I did experience vaporization and was pumping a fuel and air mixture. Per the tech at LEAF, this condition leads to fuel pump cavitation and the chugging causes a vapor release from the carb overflow tubes. And, yes, Larry, the engine did stumble when I smelled the fumes.
As I have said, if the condition occurs again, I will check the floats and most likely replace the fuel pump.
New fuel pump is the fix
After several weeks of pursuing many possibilities, I finally punted and ordered a replacement engine-driven pump. I had experienced partial power losses on take-off and substantial fluctuations in fuel pressure and fuel flow in-flight.
Because Rotax insisted that total failure of the pump (e.g. conspicuous leaking of fuel from the weep holes) was the only remedy for warrranty replacement, I had resisted throwing this particular part at my problem. Common sense told me a weak spring or leaking check valve could produce the symptoms. The fact that Rotax was actively seeking an improved model fuel pump wasn't lost on me either.
A one-hour post-installation flight showed steady FP in the mid-green and generally proper behavior with power changes. I publicly apologize to all the RV-12'ers who told me this was the problem in the first place.
Jim
RV12 #264 back in the air
After several weeks of pursuing many possibilities, I finally punted and ordered a replacement engine-driven pump. I had experienced partial power losses on take-off and substantial fluctuations in fuel pressure and fuel flow in-flight.
Because Rotax insisted that total failure of the pump (e.g. conspicuous leaking of fuel from the weep holes) was the only remedy for warrranty replacement, I had resisted throwing this particular part at my problem. Common sense told me a weak spring or leaking check valve could produce the symptoms. The fact that Rotax was actively seeking an improved model fuel pump wasn't lost on me either.
A one-hour post-installation flight showed steady FP in the mid-green and generally proper behavior with power changes. I publicly apologize to all the RV-12'ers who told me this was the problem in the first place.
Jim
RV12 #264 back in the air
Got the last one on the shelf at Lockwood. LEAF was out of stock. But still no word to us peasants on when the new--hopefully improved--models will land in the U.S. Keeping my fingers crossed this one doesn't go south before my Visa Card limit is upped enough to pay for the new one.
